WASHINGTON (AP) — Federal health regulators have approved the first pill to treat the underlying causes of multiple sclerosis, a debilitating nervous system disorder that has traditionally been treated with injectable drugs.

The Food and Drug Administration approved Swiss drugmaker Novartis' treatment Gilenya to reduce relapses in patients with multiple sclerosis, who experiences loss of balance, muscle spasms and other movement problems.

There is no cure for the disease, but steroids can reduce the duration and severity of symptoms in the short term, and seven treatments on the market have had success in reducing recurrence of symptoms.

All involve daily or regular injections, which doctors say discourages some patients from keeping up with their treatment.

"Many people prefer to take a capsule because they don't like to stick needles into themselves," said Dr. Nick LaRocca, of the National Multiple Sclerosis Society.

Since starting on Gilenya more than two years ago, Seth Morgan of Chevy Chase, Md., says he has been free of disease relapses. Morgan previously injected himself with a medication every other day.

"People say you get used to the side effects — the discomfort and burning around the injection site — but the fact of the matter is I never did," said Morgan, who worked as a neurologist before being diagnosed with the disease.

Multiple sclerosis causes the body's immune system to attack the protective coatings of the brain and spinal cord. Gilenya works to reduce a type of white blood cell that often attacks the nervous system.

The FDA approved another pill-based drug for multiple sclerosis patients earlier this year. However, that drug from Acorda Therapeutics is designed to improve walking ability, rather than treat the underlying disease.

"Gilenya is the first oral drug that can slow the progression of disability and reduce the frequency and severity in MS," said the FDA's director of neurology products, Russell Katz.

The FDA reviewed the drug under a priority timetable reserved for groundbreaking therapies.

Despite the overwhelming endorsement, panelists also had questions about side effects and said patients should receive their first dose under doctor supervision because of a potentially dangerous drop in pulse rate.

FDA labeling for Gilenya recommends all patients be observed for six hours after receiving their first dose. The label also recommends eye examinations to spot macular edema, a side effect reported in some patients.

About 2.5 million people around the world have multiple sclerosis, with an estimated 400,000 of them in the U.S. In the most common form of the disease, patients experience periods of well-being followed by periodic relapses.

Physicians who treat multiple sclerosis are mindful of safety problems with other recent treatments for the disease. Biogen Idec's drug Tysabri was approved for the condition in November 2004 and pulled from the market the next year after cases of a rare but lethal brain inflammation in some patients. It was reintroduced in 2006 under an FDA-approved distribution program.

Novartis said it is pursuing regulatory approval in Europe and the rest of the world.